This invention relates to magnetohydrodynamic (MHD) generators and, more specifically, to an improved gaseous electrode for such generators wherein a conducting gas or plasma effluent is emitted from a side wall of the generator.
MHD generators produce electrical power by the motion of high temperature electrically conductive gases through a main MHD channel past a magnetic field oriented at an angle, usually 90.degree., with respect to the gas flow. This movement induces an electromotive force (EMF) between opposed electrodes mounted in the side walls of the generator at an angle, usually 90.degree., with respect to the magnetic field. The rapid motion of the high temperature gases, however, in many cases may seriously erode a generator's electrodes, particularly a solid electrode, as do internal electric arcs which connect the electrodes to a load. Although gaseous electrodes have been suggested in the past as a solution to this problem, it is an object of this invention to provide an improved gaseous electrode using electrically conducting gases such that the electrodes do not wear out even though they may be subjected to high density generator currents.
Gaseous electrodes have previously been suggested wherein an arc is caused to move from place to place within a cavity along one or more openings in the electrode. The arc ionizes the gas in the immediate vicinity of the moving arc thereby filling the electrode cavity on the average after a certain period with ionized gas. The ionized gas is then discharged or injected into the generator's main channel to form an electrically conductive plasma plume. Such arc structures have been observed as exhibiting a cathode spot phenomenon. It has been found that the cathode spot may be caused to move from place to place by a magnetic field. It has been suggested that the longitudinal movement of the cathode spot arc can be controlled by a secondary magnetic field generated by a coil wrapped around the electrode.
Further, as an improvement over using a coil wrapped around the electrode, it has been suggested that the arc cathode spot could be caused to move back and forth in the electrode cavity in a controlled manner by positioning the electrode at an angle with respect to the MHD magnetic field. Positioning the electrode at an angle different than 90.degree. is believed to cause the arc to move in both the circumferential and longitudinal directions. The angle at which the electrode is positioned with respect to the magnetic field is known as the "yaw" angle as is more fully described in U.S. Pat. application 643,946 filed Dec. 24, 1975 and assigned to the same assignee as this application.
Such structures as described above, however, have not necessarily been as simple or reliable as might be desired. For example, since the moving arc only ionizes the gas flowing past it in a localized region in the immediate vicinity of the arc column, it is difficult to simultaneously fill the plasma effluent slot with a uniform plasma plume, necessary for the MHD current to remain in a diffuse sheet form, thereby avoiding harmful arc currents. As another example, the "yaw" angle required to move the arc column in the above design is difficult to incorporate into most MHD channel configurations.
Therefore, it is a primary object of this invention to provide a structure and method for generating a plasma plume which will cause a diffuse current rather than a localized current to flow from one electrode to an opposing electrode, without requiring a particular angle of orientation with respect to the magnetic field of the MHD generator.